The subject of the invention is an angle of rotation sensor for measurement of an angular position of a rotary shaft over more than one revolution.
From DE 41 37 092 A1 there is a known angle of rotation sensor in which an angle encoder, which can be a scanned coded disc, registers the angular position of a rotary shaft for a single revolution. A potentiometer subsequent to the coded disc registers the absolute angular position of the rotary shaft over several revolutions. A subsequent evaluation circuit combines the position of the coded disc together with the number of revolutions, under consideration of the gear-train play and measurement tolerance of the potentiometer. Angle of rotation sensors of this type always supply the absolute angle of rotation over several revolutions independently of any intermediate interruptions of the power supply. Disadvantages are the high production costs for the gear-train and sensor elements, as well as the limited durability because of the many mechanical moving parts. The number of revolutions which can be registered is limited by nature of the mechanical construction.
From DE 37 29 949 A1 there is an angle of rotation sensor known with a counting arrangement Z, several pulse-wire motion sensors S1 to S6 arranged around the circumference, and several magnets M. The outputs of the pulse-wire motion sensors are so applied to the counting arrangement that the count in the counting arrangement represents the angular position of an input wheel attached to the rotary shaft. The disadvantage of this arrangement is that the counting arrangement ceases to function with loss of power supply, such that rotation of the shaft can no longer be registered and the actual count is lost.
A known angular position sensor of this type is the product CE 100 from the company T+R, Trossingen. A fine sensor element registers the angular position of the shaft over one revolution, the measured values repeating periodically with each revolution. One or more coarse sensors are coupled subsequent to the fine sensor by means of gearing. The absolute measurement value is the result of a suitable combination of the measurements from the fine and the coarse sensor elements. Angular position sensors of this type supply the absolute angle of rotation over a large number of revolutions, independently of any intermediate interruption of the power supply. Disadvantages are the high production costs for the gear-train and the sensor elements, as well as the limited durability because of the many mechanical moving parts. The number of revolutions which can be registered is limited by the nature of the mechanical construction.
A further angle of rotation sensor of the stated type is known from the product OAM-74-11/24 bit-LPS-5V (TS5778N10) from the Tamagawa Seiko Company, Tokio. A measurement arrangement registers the angular movement of a rotary shaft. By means of a counter, incremental shaft movements are summed over several rotations under consideration of the direction of rotation to provide an absolute value. On loss of supply voltage, the operation of the angle of rotation sensor is maintained by means of a buffer battery. Long interruptions in the voltage supply during stoppages also have to be bridged by the buffer battery. The cost of realising this form of sensor is less than that for gear-coupled angle sensor elements. The disadvantage of this arrangement is the limited life of the buffer batteries. These need to be replaced at regular intervals. A further disadvantage is the necessity to supply the sensor element from a buffer battery and the associated additional battery load. Under extreme environmental conditions such as high or low temperature batteries cannot be used.